A series of bimetallic ammonium RbEu nitrates exhibiting switchable dielectric constant and photoluminescence properties

Abstract

A series of RbEu bimetallic ammonium metal nitrate hybrid analogues, [(CH₃)₃NCH₂X]₂[RbEu(NO₃)₆] (X = Cl, 1; Br, 2; I, 3), have been synthesized via solvent evaporation. This series shows similar cage-like perovskite frameworks, in which the cations are confined in the spaces enclosed by the hydrogen-bonding interactions. They display structural phase transitions between 200–430 K. Detailed single-crystal structural analysis of 1–3 reveals the change of the dynamics of the cation and the distortion of the [Rb₄Eu₄(NO₃)₁₂] anionic framework is the driving force for the structural phase transition. Meanwhile, the thermal and dielectric anomalies are verified by differential scanning calorimetry and dielectric measurements, respectively. Interestingly, the subtle change of cation significantly affects the switching temperature and dielectric behaviors, showing the typical ‘butterfly effect’ in these RbEu bimetallic hybrids. Notably, they also display excellent optical properties, that is, the Eu³⁺ ion acts as the activator of the photoluminescence property. Meanwhile, compounds 1–3 have phosphorescent characteristics and 1 has the highest fluorescence quantum yield (FQY) of 57.82%. This finding will be evidently meaningful for exploring high-performance multifunctional switching materials for novel applications.